Fluid coke contaminated catalyst regeneration process

ABSTRACT

A catalyst regeneration process and apparatus for the oxidative removal of coke from a coke-contaminated fluid catalyst. Simultaneous production of hot regenerated catalyst and a relatively-cooler flue gas is provided. The process comprises a high temperature coke combustion zone, and a lower temperature heat removal zone. Coke contaminated catalyst, oxygen containing gas and regenerated catalyst from the heat removal zone are contacted in the high temperature combustion zone, the temperature of which is controlled by adjusting the rate at which catalyst is recycled from the heat removal zone. Catalyst may be withdrawn from the top of the combustion zone and sent to the reaction zone at the controlled combustion zone temperature, the remainder of the catalyst and the hot flue gas pass to the upper heat removal zone, where both gas and catalyst are cooled, preferably by utilizing the catalyst as a heat transfer medium in a dense-phase heat exchange system. The optimum temperature may be achieved by mixing regenerated catalyst from the two zones, and 0-100% of regenerated catalyst may be withdrawn from either of the two zones. The temperature in the upper zone can be adjusted by changing the level of the dense bed in the heat removal zone, and this would be used for making gross changes in the quantity of the heat removed from the process.

BACKGROUND OF THE INVENTION

The field of art to which this invention pertains is fluid catalystregeneration. It relates to the rejuvenation of particulated-solid,fluidizable catalyst which has been contaminated by the depositionthereupon of coke. The present invention will be most useful in aprocess for regenerating coke-contaminated fluid cracking catalyst, butit should find use in any process in which coke is burned from a solid,particulated, fluidizable catalyst.

DESCRIPTION OF THE PRIOR ART

The fluid catalytic cracking process (hereinafter FCC) has beenextensively relied upon for the conversion of starting materials, suchas vacuum gas oils, and other relatively heavy oils, into lighter andmore valuable products. FCC involves the contact in a reaction zone ofthe starting material, whether it be vacuum gas oil or another oil, witha finely divided, or particulated, solid, catalytic material whichbehaves as a fluid when mixed with a gas or vapor. This materialpossesses the ability to catalyze the cracking reaction, and in soacting it is surface-deposited with coke, a by-product of the crackingreaction. Coke is comprised of hydrogen, carbon and other material suchas sulfur, and it interferes with the catalytic activity of FCCcatalysts. Facilities for the removal of coke from FCC catalyst,so-called regeneration facilities or regenerators, are ordinarilyprovided within an FCC unit. Regenerators contact the coke-contaminatedcatalyst with an oxygen-containing gas at conditions such that the cokeis oxidized and a considerable amount of heat is released. A portion ofthis heat escapes the regenerator with flue gas, comprised of excessregeneration gas and the gaseous products of coke oxidation, and thebalance of the heat leaves the regenerator with the regenerated, orrelatively coke-free, catalyst. Regenerators operating atsuperatmospheric pressures are often fitted with energy-recoveryturbines which expand the flue gas as it escapes from the regeneratorand recover a portion of the energy liberated in the expansion.

The fluidized catalyst is continuously circulated from the reaction zoneto the regeneration zone and then again to the reaction zone. The fluidcatalyst, as well as providing catalytic action, acts as a vehicle forthe transfer of heat from zone to zone. Catalyst exiting the reactionzone is spoken of as being "spent", that is partially deactivated by thedeposition of coke upon the catalyst. Catalyst from which coke has beensubstantially removed is spoken of as "regenerated catalyst."

The rate of conversion of the feed stock within the reaction zone iscontrolled by regulation of the temperature, activity of catalyst andquantity of catalyst (i.e. catalyst to oil ratio) therein. The mostcommon method of regulating the temperature is by regulating the rate ofcirculation of catalyst from the regeneration zone to the reaction zonewhich simultaneously increases the catalyst/oil ratio. That is to say,if it is desired to increase the conversion rate an increase in the rateof flow of circulating fluid catalyst from the regenerator to thereactor is effected. Inasmuch as the temperature within the regenerationzone under normal operations is invariably higher than the temperaturewithin the reaction zone, this increase in influx of catalyst from thehotter regeneration zone to the cooler reaction zone effects an increasein reaction zone temperature. It is interesting to note that: thishigher catalyst circulation rate is sustainable by virtue of the systembeing a closed circuit; and, the higher reactor temperature issustainable by virtue of the fact that increased reactor temperatures,once effected, produce an increase in the amount of coke being formed inthe reaction and deposited upon the catalyst. This increased productionof coke, which coke is deposited upon the fluid catalyst within thereactor, provides, upon its oxidation within the regenerator, anincreased evolution of heat. It is this increased heat evolved withinthe regeneration zone which, when conducted with the catalyst to thereaction zone, sustains the higher reactor temperature operation.

Recent, politico-economic restraints which have been put upon thetraditional lines of supply of crude oil have made necessary the use, asstarting materials in FCC units, of heavier-than-normal oils. FCC unitsmust now cope with feed stocks such as residual oils and in the futuremay require the use of mixtures of heavy oils with coal or shale derivedfeeds.

The chemical nature and molecular structure of the feed to the FCC unitwill affect that level of coke on spent catalyst. Generally speaking,the higher the molecular weight, the higher the Conradson carbon, thehigher the heptane insolubles, and the higher the carbon to hydrogenratio, the higher will be the coke level on the spent catalyst. Alsohigh levels of combined nitrogen, such as is found in shale derivedoils, will also increase the coke level on spent catalyst. Theprocessing of heavier and heavier feedstocks, and particularly theprocessing of deasphalted oils, or direct processing of atmosphericbottoms from a crude unit, commonly referred to as reduced crude, doescause an increase in all or some of these factors and does thereforecause an increase in coke level on spent catalyst.

This increase in coke on spent catalyst results in a larger amount ofcoke burnt in the regenerator per pound of catalyst circulated. Heat isremoved from the regenerator in conventional FCC units in the flue gasand principally in the hot regenerated catalyst stream. An increase inthe level of coke on spent catalyst will increase the temperaturedifference between the reactor and the regenerator, and in theregenerated catalyst temperature. A reduction in the amount of catalystcirculated is therefore necessary in order to maintain the same reactortemperature. However, this lower catalyst circulation rate required bythe higher temperature difference between the reactor and theregenerator will result in a fall in conversion, making it necessary tooperate with a higher reactor temperature in order to maintainconversion at the desired level. This will cause a change in yieldstructure which may or may not be desirable, depending on what productsare required from the process. Also there are limitations to thetemperatures that can be tolerated by FCC catalyst without there being asubstantial detrimental effect on catalyst activity. Generally, withcommonly available modern FCC catalyst, temperatures of regeneratedcatalyst are usually maintained below 1350° F., since loss of activitywould be very severe above 1400°-1450° F. Also, energy recoveryturbines, sometimes called "power recovery turbines," commonly cannottolerate flue gas at temperatures in excess of 1300° F.-1350° F. If arelatively common reduced crude such as that derived from Light Arabiancrude oil were charged to a conventional FCC unit, and operated at atemperature required for high conversion to lighter products, i.e.,similar to that for a gas oil charge, the regenerator temperature wouldoperate in the range of 1600°-1800° F. This would be too high atemperature for the catalyst, require very expensive materials ofconstruction, and give an extremely low catalyst circulation rate. It istherefore accepted that when materials are processed that would giveexcessive regenerator temperatures, a means must be provided forremoving heat from the regenerator, which enables a lower regeneratortemperature, and a lower temperature difference between the reactor andthe regenerator.

Prior art methods of heat removal generally provide coolant-filled coilswithin the regenerator, which coils are in contact either with thecatalyst from which coke is being removed or with the flue gas justprior to the flue gas' exit from the regenerator. For example, McKinneyU.S. Pat. No. 3,990,992 discloses a fluid catalytic cracking processdual zone regenerator with cooling coils mounted in the second zone. Thesecond zone is for catalyst disengagement prior to passing the flue gasfrom the system, and contains catalyst in a dilute phase. Coolantflowing through the coils absorbs heat and removes it from theregenerator.

These prior art coils have been found to be inflexible in that they areusually sized to remove the quantity of heat which will be liberated bythe prospective feed stock which is most extensively coke-forming.Difficulties arise when a feed stock of lesser coke-formingcharacteristics is processed. In such a case the heat-removal coils arenow oversized for the job at hand. They, consequently, remove entirelytoo much heat. When heat removal from the regenerator is higher thanthat required for a particular operation, the temperature within theregenerator is depressed. This leads to a lower than desired temperatureof regenerated catalyst exiting the regenerator. The catalystcirculation rate required to obtain the desired reaction zonetemperature will increase, and may exceed the mechanical limitations ofthe equipment. The coke production rate will be higher than necessary onthis feedstock, and the lower temperature will result in less efficientcoke burning in the regeneration zone, with a greater amount of residualcoke on regenerated catalyst. Such are the operational difficultiescaused by prior art heat removal means due to their inflexibility.

Indeed, these prior art heat removal schemes also significantlycomplicate the start-up of prior art units. The presence of inflexibleheat removal coils within the coke-oxidizing section of the regeneratoroften drastically extends the time period required for raising theregenerator to its operational temperature level.

Like the basic concept of heat removal from FCC regenerators, the basicconcept of internal and external recycle of catalyst particles in FCCregenerators is not, per se, novel. Examples of such concepts are taughtin Gross et al U.S. Pat. No. 4,035,284, Pulak U.S. Pat. No. 3,953,175,Strother U.S. Pat. No. 3,898,050, Conner et al U.S. Pat. No. 3,893,812,Pulak U.S. Pat. No. 4,032,299, Pulak U.S. Pat. No. 4,033,728, and PulakU.S. Pat. No. 4,065,269. The catalyst recycle schemes taught by thesereferences, however, even when considered in the light of the prior artmethods of heat removal, as discussed above, do not and are not able toachieve the simultaneous provision of flue gas cool enough for powerrecovery, a close control of the temperatures of the various regeneratedcatalyst streams and the control of heat removal from the regenerator.

The regeneration process and apparatus which I hereby disclose offer theadvantages of an easier and quicker start-up, the maintenance of fluegas cool enough for power recovery, the provision of regeneratedcatalyst hot enough to maintain desired feed stock conversion rates inthe reaction zone with reasonable catalyst circulation rates, and facilecontrol of both the regenerated catalyst temperature and the extent ofheat removal from the regenerator. My invention involves the combinationof a combustion zone, a heat removal zone and paths provided for theinternal and/or external recycle of streams of catalysts individuallywithdrawn from the zones.

SUMMARY OF THE INVENTION

Accordingly, the objectives of my invention are to provide in a processfor regenerating a coke-contaminated fluid catalyst (1) a close controlof the temperature in the upper part of the combustion zone by thecontrol of the recirculation of regenerated caytalyst from which heathas been removed to the combustion zone; (2) heat removal from theregenerator and close control thereof by manipulating the extent ofimmersion of heat removal means in a dense-phase fluid bed of theregenerator; (3) close control of the temperature of the regeneratedcatalyst required for circulation to the reactor by obtaining thecatalyst from either a heat removal zone of the regenerator, in which itis relatively cool, or the combustion zone of the regenerator in whichit is hottest, or as a mixture from both of these sources in relativeamounts selected to impart the desired temperature to the mixture; and(4) a combination of the first and third of the above stated objectives.It is another objective to provide a regeneration apparatus uniquelysuited for use in the practice of my regeneration process.

My invention is, in one embodiment, a process for regenerating acoke-contaminated fluid catalyst, said process including the steps of:

(a) introducing oxygen-containing regeneration gas and coke-contaminatedfluid catalyst into a lower locus of a combustion zone maintained at atemperature sufficient for coke-oxidation and therein oxidizing coke toproduce hot regenerated catalyst and hot flue gas;

(b) transporting said hot flue gas and a portion of said hot regeneratedcatalyst into a lower locus of a heat removal zone and thereinmaintaining said catalyst at dense-phase fluid bed conditions; and

(c) withdrawing heat from said hot regenerated catalyst in said heatremoval zone to produce cooler regenerated catalyst; which process hasthe improvement which comprises the control of the temperature at anupper locus of said combustion zone by withdrawing at least a portion ofsaid cooler regenerated catalyst from said heat removal zone andintroducing said portion of cooler regenerated catalyst into saidcombustion zone.

In a second embodiment, my invention is an apparatus for regenerating acoke-contaminated, fluid catalyst, which apparatus comprises incombination:

(a) a vertically-oriented combustion chamber;

(b) a spent catalyst inlet conduit for gas and fluid catalyst connectingwith the lower portion of said combustion chamber;

(c) a heat removal chamber located superadjacent to said combustionchamber and in communication therewith;

(d) heat removal means disposed within said heat removal chamber;

(e) a catalyst withdrawal conduit connected at one end to said heatremoval chamber for withdrawing regenerated fluid catalyst from saidheat removal chamber; and

(f) a catalyst recycle conduit connecting said withdrawal conduit withthe lower portion of said combustion chamber, such that fluid catalystcan pass from said heat removal chamber to said combustion chamber.

In a third embodiment, my invention is a process for regenerating acoke-contaminated fluid catalyst, said process including the steps of:

(a) introducing oxygen-containing regeneration gas and coke-contaminatedfluid catalyst into a lower locus of a combustion zone maintained at atemperature sufficient for coke-oxidation and therein oxidizing coke toproduce hot regenerated catalyst and hot flue gas;

(b) transporting said hot flue gas and a portion of said hot regeneratedcatalyst into a lower locus of a heat removal zone and thereinmaintaining said catalyst at dense-phase fluid bed conditions; and

(c) withdrawing heat from said hot regenerated catalyst in said heatremoval zone to produce cooler regenerated catalyst; which process hasthe improvement which comprises the control of the amount of heatremoval in the heat removal zone and thereby the temperature of theregenerated catalyst in the dense-phase fluid bed of said heat removalzone by: (1) providing heat-removal means partially immersed in saiddense-phase fluid bed of the heat removal zone; and (2) manipulating theextent of immersion of said heat removal means in said dense-phase fluidbed.

In a fourth embodiment, my invention is an apparatus for regenerating acoke-contaminated, fluid catalyst, which apparatus comprises incombination:

(a) a vertically-oriented combustion chamber;

(b) a spent catalyst inlet conduit for gas and fluid catalyst connectingwith the lower portion of said combustion chamber;

(c) a heat removal chamber located superadjacent to said combustionchamber and in communication therewith;

(d) heat removal means disposed within said heat removal chamber;

(e) a catalyst withdrawal conduit connected at one end to said heatremoval chamber for withdrawing regenerated fluid catalyst from saidheat removal chamber; and

(f) means for manipulating the extent of immersion of said heat removalmeans in a fluidized catalyst bed disposed within said heat removalchamber.

In a fifth embodiment, my invention is a process for regenerating acoke-contaminated fluid catalyst, said process including the steps of:

(a) introducing oxygen-containing regeneration gas and coke-contaminatedfluid catalyst into a lower locus of a combustion zone maintained at atemperature sufficient for coke-oxidation and therein oxidizing coke toproduce hot regenerated catalyst and hot flue gas;

(b) collecting and withdrawing from an upper locus of said combustionzone a portion of said hot regenerated catalyst;

(c) transporting said hot flue gas and the remaining portion of said hotregenerated catalyst into a lower locus of a heat removal zone andtherein maintaining said catalyst at dense-phase fluid bed conditions;and

(d) withdrawing heat from said hot regenerated catalyst in said heatremoval zone to produce cooler regenerated catalyst; which process hasthe improvement which comprises obtaining required regenerated catalystat any desired temperature within or at a limit of a temperature rangethe lower limit of which is the temperature of said cooler regeneratedcatalyst and the upper limit of which is the temperature of said hotregenerated catalyst, by: (1) withdrawing the required regeneratedcatalyst exclusively from said heat removal zone if the desiredtemperature is the lower limit of said temperature range; (2)withdrawing the required regenerated catalyst exclusively from saidupper locus of said combustion zone if the desired temperature is theupper limit of said temperature range; (3) withdrawing a portion of therequired regenerated catalyst from said heat removal zone, withdrawingthe remaining portion from said upper locus of said combustion zone, andmixing said portions in proportions selected to achieve the desiredtemperature, if said desired temperature lies within said upper andlower limits of said temperature range.

In a sixth embodiment, my invention is an apparatus for regenerating acoke-contaminated, fluid catalyst which apparatus comprises incombination:

(a) a vertically-oriented combustion chamber;

(b) a spent catalyst inlet conduit for gas and fluid catalyst connectingwith the lower portion of said combustion chamber;

(c) fluid catalyst collecting means disposed within an upper portion ofsaid combustion chamber;

(d) a first catalyst withdrawal conduit, connecting with said catalystcollecting means, for withdrawal of collected regenerated fluid catalystfrom said combustion chamber;

(e) a heat removal chamber located superadjacent to said combustionchamber and in communication therewith;

(f) heat removal means disposed within said heat removal chamber;

(g) a second catalyst withdrawal conduit for withdrawing regeneratedfluid catalyst from said heat removal chamber; and

(h) a mixing conduit connected at one end to said second withdrawalconduit and at the other end to said first withdrawal conduit, such thatregenerated fluid catalyst from said heat removal chamber can pass intosaid first withdrawal conduit.

In a seventh embodiment, my invention is a process for regenerating acoke-contaminated fluid catalyst, said process including the steps of:

(a) introducing oxygen-containing regeneration gas and coke-contaminatedfluid catalyst into a lower locus of a combustion zone maintained at atemperature sufficient for coke-oxidation and therein oxidizing coke toproduce said hot regenerated catalyst and hot flue gas;

(b) collecting and withdrawing from an upper locus of said combustionzone a portion of said hot regenerated catalyst;

(c) transporting said hot flue gas and the remaining portion of said hotregenerated catalyst into a lower locus of a heat removal zone andtherein maintaining said catalyst at dense-phase fluid bed conditions;

(d) withdrawing heat from said hot regenerated catalyst in said heatremoval zone to produce cooler regenerated catalyst; which process hasthe improvement which comprises: (a) the control of the temperature ofsaid upper locus of said combustion zone by withdrawing at least aportion of said cooler regenerated catalyst from said heat removal zoneand introducing said portion of cooler regenerated catalyst into saidcombustion zone; (b) obtaining required regenerated catalyst at anytemperature within or at a limit of a temperature range, the lower limitof which is the temperature of said cooler regenerated catalyst and theupper limit of which is the temperature of said hot regeneratedcatalyst, by: (1) withdrawing the required regenerated catalystexclusively from said heat removal zone if the desired temperature isthe lower limit of said temperature range; (2) withdrawing the requiredregenerated catalyst exclusively from said upper locus of saidcombustion zone if the desired temperature is the upper limit of saidtemperature range; (3) withdrawing a portion of the required regeneratedcatalyst from said heat removal zone, withdrawing the remaining portionfrom said upper locus of said combustion zone and mixing said portionsin proportions selected to achieve said desired temperature, if saiddesired temperature lies within said upper and lower limits of saidtemperature range.

In an eighth embodiment, my invention is an apparatus for regenerating acoke-contaminated, fluid catalyst, which apparatus comprises incombination:

(a) a vertically-oriented combustion chamber;

(b) a spent catalyst inlet conduit for gas and fluid catalyst connectingwith the lower portion of said combustion chamber;

(c) fluid catalyst collecting means situated at an upper portion of saidcombustion chamber;

(d) a first catalyst withdrawal conduit, connecting with said fluidcatalyst collecting means, for withdrawal of collected regenerated fluidcatalyst from said combustion chamber;

(e) a heat removal chamber located superadjacent to said combustionchamber and in communication therewith;

(f) heat removal means disposed within said heat removal chamber;

(g) a second catalyst withdrawal conduit connected at one end to saidheat removal chamber for withdrawing regenerated fluid catalyst fromsaid heat removal chamber;

(h) a catalyst recycle conduit connecting said second withdrawal conduitwith the lower portion of said combustion chamber, such that regeneratedfluid catalyst can pass from said heat removal chamber to saidcombustion chamber; and

(i) a mixing conduit connected at one end to said second withdrawalconduit and at the other end to said first withdrawal conduit such thatregenerated fluid catalyst from said heat removal chamber can pass intosaid first withdrawal conduit.

Other embodiments and objects of the present invention encompass furtherdetails such as process streams and the function and arrangement ofvarious components of my apparatus, all of which are hereinafterdisclosed in the following discussion of each of these facets of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional, elevation view of a regeneration apparatusaccording to the present invention, showing combustion zone 1 and heatremoval zone 2, recycle conduit 18, 20 and mixing conduit 33.

FIG. 2 is an enlarged sectional view of combustion zone 1, fluidcatalyst collecting means 8 and second mixing conduit 26'.

FIG. 3 is another enlarged, sectional view of combustion zone 1, showingsecond recycle conduit 29, 31.

Referring now to FIG. 1, a regenerator is shown which includesvertically-oriented combustion zone 1 in association with heat removalzone 2. Coke-contaminated catalyst enters the regenerator throughconduit 4, after having passed through flow control valve 5.Regeneration gas enters the system in conduit 3 and combines withcoke-contaminated catalyst in conduit 4 and regenerated catalyst inconduit 20 before passing to distributor 6 located in the lower part ofcombustion zone 1. The combination of conduits 20, 3 and 4 anddistributor 6 are referred to herein as an "inlet for gas and catalyst."

A mixture of regeneration gas, regenerated catalyst andcoke-contaminated catalyst exit distributor 6 and pass upwardly withincombustion zone 1. Conditions within the combustion zone are such thatthe regeneration gas and coke combine chemically to form flue gas,leaving the catalyst relatively free from coke.

Fluid catalyst collecting means 8 is situated in an upper part ofcombustion zone 1 and in the proximity of surface 7 and passageway 11. Aportion of regenerated catalyst within the combustion zone is collectedby fluid catalyst collecting means 8 and exits the combustion zonethrough withdrawal conduit 9 and control valve 10. Any catalystcollected in means 8, in excess of that withdrawn through conduit 9,will overflow back into the combustion zone and be re-entrained by thecombustion gas. The remaining portion of regenerated catalyst withincombustion zone 1, not withdrawn through conduit 9, exits the combustionzone with flue gas through passageway 11 and impinges upon deflector 12,which serves to distribute the flue gas to the dense-phase fluidized bedin the heat removal zone.

Heat removal zone 2 is located above combustion zone 1 and communicatestherewith through passageway 11. Situated within heat removal zone 2are: heat removal means 21; means 14, 15 for withdrawing fluid catalyst;collecting means 17 and recycle conduit 18,20; dense-phase fluidcatalyst bed 13; and gas-catalyst separation means 23. Pressuresensitive devices 35 and 37 connect with level sensing, recording andcontrol device 34 by way of lines 36 and 38, respectively. Level sensingand control device 34 connects to flow control valve 5 by way of line39. Temperature recorder control device 42 connects to temperaturesensing device 40 by way of line 41, and connects to control valve 19 byway of line 43. Temperature recorder control device 44 connects totemperature sensing device 47 by way of line 45, and connects to controlvalve 32 by way of line 46.

Flue gas and regenerated catalyst, having entered heat removal zone 2through passageway 11, intermingle with particulated catalyst indense-phase fluid bed 13. Means 14, 15 for withdrawing fluid catalysthaving associated with them flow control valve 16 for the control of therate of catalyst withdrawal. The surface level of fluid bed 13 may beraised or lowered indirectly by reducing or increasing the flow,respectively, through flow control valve 5. Level sensing, recording andcontrol device 34 determines the level of the dense-phase catalyst bed13 based on the differentials in pressures measured by pressuresensitive devices 35 and 37. Variations in bed density and/or depth ofbed within the dense-phase region will be reflected in a varyingpressure differential. Device 34 will then maintain a predeterminedlevel in dense-phase bed 13 by controlling control valve 5. Raising orlowering the level of fluid bed 13 increases or decreases, respectively,the extent of immersion of heat removal means 21 in bed 13. Flue gasexits bed 13, entraining therewith a small amount of regeneratedcatalyst, and enters inlet 22 of separation means 23 where the entrainedcatalyst is disengaged from the flue gas. Flue gas, now separated fromthe priorly entrained catalyst, exits heat removal zone 2 through outlet24. Priorly-entrained catalyst returns to fluid bed 13 from separationmeans 23 in conduits 25 and 26.

Recycle conduit 18, fitted with control valve 19, is provided in orderthat a flow of catalyst from dense-phase fluid bed 13 to regenerationgas inlet 3 may be established and regulated. Temperature recordercontrol device 42 determines the temperature of the catalyst in conduit9 and controls control valve 19 in response thereto so as to achieve apredetermined temperature setting.

Mixing conduit 33 is provided for communication between conduit 15 andconduit 9, such that catalyst withdrawn from heat removal zone 2 inconduit 15 may pass, through control valve 32, into conduit 9 downstreamof control valve 10. Temperature recorder control device 44 determinesthe temperature of the catalyst in conduit 9 and controls control valve32 in response thereto so as to achieve a predetermined temperaturesetting.

Turning now to FIG. 2, second mixing conduit 26', 28 and control valve27 are shown. This second mixing conduit is provided to accommodate aflow of regenerated catalyst from withdrawal conduit 9 tocoke-contaminated catalyst conduit 4.

Proceeding to FIG. 3, the alternative recycle conduit 29, 31, having afixed flow regulating means 30, is indicated. The alternative recycleconduit is provided to furnish a flow path for regenerated catalyst fromfluid catalyst collecting means 8, internally within combustion zone 1,to a lower part of the combustion zone.

The above-described drawings are intended to be schematicallyillustrative of my invention and not be limitations thereon.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, in its process aspects, consists of steps for theregenerative combustion within a combustion zone of thecoke-contaminated catalyst from a reaction zone to form hot flue gas andhot regenerated catalyst, collection and withdrawal of a portion of thehot regenerated catalyst, cooling of another portion of the hotregenerated catalyst within a heat removal zone, cooling of hot flue gaswithin the heat removal zone, using the cooled regenerated catalyst as aheat sink, and the use of portions of hot regenerated catalyst andcooled regenerated catalyst for control of the temperatures of thecombustion zone and the regenerated catalyst stream to be returned tothe reaction zone.

Reference will now be made to the attached drawings for a discussion ofthe regeneration process and apparatus of my invention. In FIG. 1regeneration gas, which may be air or another oxygen-containing gas,enters in conduit 3 and mixes with coke-contaminated catalyst enteringin conduit 4 and regenerated catalyst in conduit 20. The resultantmixture of coke-contaminated catalyst, regenerated catalyst andregeneration gas are distributed into the interior of combustion zone 1,at a lower locus thereof, by distributor 6. Coke-contaminated catalystcommonly contains 0.1 to 5 wt. % carbon, as coke. Coke is predominantlycomprised of carbon, however, it can contain from 5 to 15 wt. %hydrogen, as well as sulfur and other materials. The regeneration gasand entrained catalyst flows upward from the lower part of combustionzone 1 to the upper part thereof. While it is not critical to thepractice of this invention, it is believed that dilute phase conditions,that is a catalyst/gas mixture of less than 30 lbs. per cubic foot, andtypically 2-10 lbs. per cubic foot, are the most efficient for cokeoxidation. As the catalyst/gas mixture ascends within combustion zone 1the heat of combustion of coke is liberated and absorbed by the nowrelatively carbon-free catalyst, in other words by the regeneratedcatalyst.

The rising catalyst/gas stream impinges upon surface 7, whichimpingement changes the direction of flow of the stream. It is wellknown in the art that impingement of a fluidized particulate stream upona surface, causing the stream to turn through some angle, can result inthe separation from the stream of a portion of the solid materialtherein. The impingement of the catalyst-gas stream upon surface 7within combustion zone 1 causes a portion of the hot regeneratedcatalyst flowing in the combustion zone to collect within fluid catalystcollecting means 8. Means 8 may be a cone-shaped receptacle, as shown,or any other shape appropriate for collecting catalyst particles. Thegaseous products of coke oxidation and excess regeneration gas, of fluegas, and the uncollected portion of hot regenerated catalyst flowthrough passageway 11 and enter fluidized bed 13 within superadjacentheat removal zone 2. The density of the catalyst-gas mixture within bed13 is preferably maintained at 30 lbs. per cubic foot or higher and itis therefore characterized as a dense-phase fluid bed.

I prefer the maintenance of a dense-phase fluid bed within the heatremoval zone, rather than a dilute-phase fluid bed, because dense-phaseconditions afford greatly increased heat transfer rates from the bed ofheat removal means 21. Heat removal means 21 are provided to withdrawheat from the dense-phase bed. In a preferred embodiment of my inventionthe heat removal means comprise conduits of substantially verticalorientation, the interiors of which conduits are sealed from theinterior of the heat removal zone, and which conduits have flowingtherein a heat-absorbing material, such as water. The objective is toabsorb heat into the heat-absorbing material through its indirectcontact with dense-phase fluid bed 13. As the heat transfer coefficientis much higher for the section of the tubes immersed in the fluidizedbed, than for the section of tubes above the bed, changing the extent ofimmersion will change the amount of heat removed. The immersion of heatremoval means 21 may be varied by any suitable means, including thevertical displacement of the heat removal means with respect to thedense-phase bed or the variation in regenerated catalyst inventorywithin the heat removal zone. In this embodiment the surface of fluidbed 13, and therefore the extent of immersion of heat removal means 21,is controlled through the action of control valve 5, and the resultingfluctuations of the catalyst level in the reactor or reactor catalyststripper are permitted. However, when widely different feedstocks areprocessed, producing widely different amounts of coke, and as a resultrequiring widely different heat removal from the regenerator, it isforeseen that additional catalyst would be added to the unit in order toallow a substantial increase in the level of bed 13, without losing thecatalyst level entirely in the associated reactor or reactor catalyststripper. It should also be understood that it will not be necessary tomake changes in the catalyst inventory of the heat removal zone toaccommodate relatively small changes in the coke level on spentcatalyst, as would be encountered when changing between two relativelysimilar reduced crude feeds, or as might be caused by some change inoperating conditions within the reactor section, or slight change infeed charge rate to the reactor section. If small changes in coke onspent catalyst or heat removal requirement occur, it is anticipated thatthe operating temperature in the heat removal zone would be allowed tovary over a range of say 50° F. before any adjustments of level isrequired, and this change in temperature would automatically adjust theamount of heat removed. Although the temperature in the heat removalzone may vary over a range of say 50° F., the temperature at the top ofthe combustor, and of the catalyst withdrawn through collection means 8will remain unchanged and steady at the selected control temperature.This provides a degree of freedom not previously available to the FCCoperator.

Hot regenerated catalyst within the heat removal zone contacts, and iscooled by, heat removal means 21. The cooled regenerated catalystthereafter contacts hot flue gas which is ascending through the fluidbed within the heat removal zone. This contact results in heat exchangebetween the hot flue gas and the cooler regenerated catalyst, providinga relatively-cooler flue gas. The relatively-cooler flue gas exits fluidbed 13 and enters separation means 23 through inlet 22. These separationmeans may be cyclone separators, as schematically shown in FIG. 1, orany other effective means for the separation of particulated catalystfrom a gas stream. Catalyst separated from the relatively cooler fluegas returns to dense-phase fluid bed 13 through conduits 25 and 26. Therelatively-cooler flue gas exits heat removal zone 2 via conduit 24,through which it may safely proceed to associated energy recoverysystems.

Recycle conduit 18 is attached at one end to a lower part of the heatremoval zone and at the other end to a lower part of the combustionzone. Cooler regenerated catalyst proceeds through this conduit, theflow rate being controlled by control valve 19, from heat removal zone 2to combustion zone 1 and provides a heat sink for the reduction andthereby a control of the combustion zone temperature. The flow rate ofthe cooler regenerated catalyst stream will be controlled in order tomaintain a constant temperature of the catalyst withdrawn from conduit9, or alternatively, the temperature of the mixture of flue gas andcatalyst passing through passageway 11. These temperatures will commonlybe in the range of 1300°-1400° F.

Means 14 may be provided within heat removal zone 2 for the withdrawalof cooler regenerated catalyst therefrom.

As aforesaid, the hot regenerated catalyst in conduit 9 is returned tothe reaction zone at a rate sufficient to sustain the requiretemperature within the reaction zone. It is highly desirable, therefore,that the hot regenerated catalyst temperature by controllable at anoptimum level. Operating in accordance with this invention it ispossible to select catalyst at the temperature of the combustion zone,through collection means 8, or of the heat removal zone throughcollection means 14. If neither of these temperatures are optimum forthe reactor section, then a controlled temperature intermediate betweenthese two can be achieved by utilizing conduit 33 and associated controlvalve 32. Conduit 33 which is connected at one end to the means forwithdrawing cooler regenerated catalyst from heat removal zone 2 and atthe other end to the conduit for withdrawal of hot regenerated catalyst9, is a mixing conduit as it provides a path for the introduction ofcooler regenerated catalyst into the hot regenerated catalyst stream forthe purpose of lowering the temperature of the hot regenerated catalyststream when necessary to maintain the temperature of the stream ofregenerated catalyst returning to the reaction zone. This will permitblending of catalyst from the regeneration and heat removal zones, inorder to obtain a catalyst stream for return to the reactor at atemperature intermediate between the temperature of regeneration andheat removal zones. This mode of operation is suggested as analternative to the other options of withdrawing 100% of the catalystfrom either of the two zones, or of having separate inlets to thereactor riser for the regenerated catalyst from each zone.

Reiterating, it is often desirable that the temperature within thecombustion zone be amenable to control at a preselected, constant level.Conduit 18 has been provided for the introduction to combustion zone 1of cooler regenerated catalyst in order to suppress and control thetemperature within the combustion zone.

It may also be desirable to provide an affirmative method for minimizingthe temperature rise across the combustion zone. This will result in alower temperature rise across the regeneration zone, and the higheraverage combustion temperature could be used in order to obtain greaterregeneration efficiency. FIG. 2 indicates the provision of second mixingconduit 26', 28 and associated flow control valve 27. This second mixingconduit provides for the recycle of hot regenerated catalyst, a part ofthat collected in the upper locus of the combustion zone by collectingmeans 8, to a lower locus of the combustion zone. Such recycle of hotregenerated catalyst to the relatively cooler, lower region of thecombustion zone provides a heat input which raises the temperature ofthe lower region of the combustion zone.

Another manner of effecting a minimum temperature rise across thecombustion zone and an increased lower combustion zone temperature isshown in FIG. 3. Hot regenerated catalyst which has been collected bymeans 8 at a relatively hotter, upper locus of the combustion zone maybe returned directly to a relatively cooler lower locus of thecombustion zone to raise the temperature therein. FIG. 3 indicates asecond recycle conduit, designated as item 29, 31. The second recycleconduit is connected at one end to fluid catalyst collecting means 8,and the other end is in open communication with a lower locus of thecombustion zone. Also shown in FIG. 3 is flow restricting means 30situated in the second recycle conduit. Such a flow restricting deviceis desirable for the purpose of controlling the extent of increase ofcombustion zone temperature by control of the rate of internal recycleof hot regenerated catalyst through the second recycle conduit. Item 30may be a flow control valve, a restriction orifice, or any otherappropriate flow-varying means.

ILLUSTRATIVE EMBODIMENT

The following example represents a particularly preferred modecontemplated for the practice of my invention, expressed in terms of themass flow rates and temperatures of streams flowing in the regeneratordepicted in attached FIG. 1. The regenerator processes spent catalystfrom a reaction zone which is cracking a reduced crude oil feed stock.In the tabulation below the streams flowing within conduits aretabulated in registry with the item numbers of the conduits shown inFIG. 1.

    __________________________________________________________________________    Stream                            lbs./hr.                                                                           °F.                             __________________________________________________________________________    4   Coke Contaminated Catalyst (from reactor)                                                                   2,724,552                                                                          1050                                       Catalyst                      2,691,362                                                                          1050                                       Coke                          30,902                                                                             1050                                   3   Regeneration Gas (air)        463,530                                                                             307                                   9   Hot Regenerated Catalyst From Upper Locus                                                                   2,691,362                                                                          1380                                       of Combustion Zone (to reactor)                                           11  Hot Regenerated Catalyst plus                                                 Hot Flue Gas                  4,114,730                                                                          1400                                       Hot Catalyst                  3,621,428                                                                          1400                                       Hot Gas                       493,302                                                                            1400                                   18,20                                                                             Recycled Cooler Regenerated Catalyst                                                                        3,621,428                                                                          1230                                       (to inlet of combustion zone)                                             24  Flue Gas                      493,302                                                                            1250                                   21  Heat Removed by Heat Removal Means - 169.17 × 10.sup.6 BTU/hr.          Heat Losses From Regenerator Vessel - 3.41 × 10.sup.6 BTU/hr.       __________________________________________________________________________

It should be noted that in this particular operation the feed stock tothe reaction zone is a reduced crude oil, a material which yields arelatively high coke production. Such a high coke production, and theconsequent, extraordinarily high evolution of heat in the combustionzone made necessary the recycle of U.S. Pat. No. 3,621,428 lbs./hr. ofcooler regenerated catalyst from the heat removal zone to the combustionzone in order to limit the maximum combustion zone temperature to 1400°F.

It should also be noted that this illustrative embodiment is presentedfor a system where all of the catalyst returned to the riser iswithdrawn from collection means 8 at 1380° F. If required, the catalystcould be withdrawn from the heat removal zone at 1230° F. This wouldresult in a substantial increase in the catalyst circulation rate to thereactor section in order to maintain the 1050° F. reaction zone shown.Furthermore, both the temperature at the top of the combustion zone andin the heat removal zone could be adjusted over a range of 100°-150° F.from the temperatures shown, by appropriate changes in heat removalsurface in the heat removal zone and circulation rates of the variousstreams shown.

No flow in conduits 26 or 29 has been shown in the illustrativeembodiment as these serve only to reduce the temperature rise across thecombustion zone and do not influence the overall heat balance of theregeneration system.

As shown in the data tabulation the hot regenerated catalyst iswithdrawn from the combustion zone at 1380° F., while the flue gas exitsthe heat removal zone at 1250° F., relatively cooler than the hotregenerated catalyst and well below the precautionary 1300° F. limit setby downstream energy recovery systems.

I claim as my invention:
 1. A process for regenerating a coke-contaminedfluid catalysts to obtain a regenerated catalyst of a predeterminedtemperature range for return of said regenerated catalyst to ahydrocarbon conversion zone which process comprises:(a) introducingoxygen-containing regeneration gas and coke-contaminated fluid catalystinto a lower locus of a relatively dilute-phase combustion zonemaintained at a temperature sufficient for coke-oxidation and thereinoxidizing coke to produce hot regenerated catalyst and hot flue gas; (b)collecting and withdrawing from an upper locus of said relativelydilute-phase combustion zone a portion of said hot regenerated catalyst;(c) transporting said hot flue gas and the remaining portion of said hotregenerated catalyst into a lower locus of a relatively dense-phase heatremoval zone and therein maintaining said catalyst at relativelydense-phase fluid bed conditions; (d) withdrawing heat by a heat-removalmeans from said hot regenerated catalyst in said relatively dense-phaseheat removal zone; and (e) recovering regenerated catalyst possessingthe predetermined temperature range for its return to said hydrocarbonconversion zone by (1) either withdrawing the required regeneratedcatalyst exclusively from said upper locus of said relativelydilute-phase combustion zone when the desired temperature of saidregenerated catalyst is the upper limit of said predetermined range; or(2) withdrawing a portion of the required regenerated catalyst from saidrelatively dense-phase heat removal zone, withdrawing a portion fromsaid upper locus of said relatively dilute-phase combustion zone andthereafter admixing said withdrawn portions in selected proportions toachieve an admixture of regenerated catalyst possessing the desiredtemperature range for return of same to said hydrocarbon conversionzone.
 2. A process for regenerating a coke-contaminated fluid catalystto obtain a regenerated catalyst of a predetermined temperature rangefor return of said regenerated catalyst to a hydrocarbon conversion zonewhich process comprises:(a) introducing oxygen-containing gas andcoke-contaminated fluid catalyst into a lower locus of a relativelydilute-phase combustion zone maintained at a temperature sufficient forcoke-oxidation and therein oxidizing coke to produce said hotregenerated catalyst and hot flue gas; (b) collecting and withdrawingfrom an upper locus of said relatively dilute-phase combustion zone aportion of said hot regenerated catalyst; (c) transporting said hot fluegas and the remaining portion of said hot regenerated catalyst into alower locus of a relatively dense-phase heat removal zone and thereinmaintaining said catalyst at relatively dense-phase fluid conditions;(d) withdrawing heat by a heat removal means from said hot regeneratedcatalyst maintained in said relatively dense phase heat removal zone;(e) controlling the temperature of said upper locus of said relativelydilute-phase combustion zone by withdrawing at least a portion of saidregenerated catalyst from said relatively dense-phase heat removal zoneand introducing said withdrawn portion into said relatively dilute-phasecombustion zone; and (f) obtaining said regenerated catalyst ofpredetermined temperature range, the lower limit of which is thetemperature of said catalyst maintained in said relatively dense-phaseheat removal zone after said desired portion of heat has been withdrawnin subparagraph (d) by either: (1) withdrawing said required regeneratedcatalyst for return to said hydrocarbon conversion zone exclusively fromsaid upper locus of said relatively dilute-phase combustion zone whenthe desired temperature range of said regenerated catalyst is the upperlimit of said predetermined temperature range; or (2) withdrawing aportion of said required regenerated catalyst from said relativelydense-phase heat removal zone, withdrawing a portion of said requiredregenerated catalyst from said upper locus of said relativelydilute-phase combustion zone and admixing said portions in proportionsto achieve a regenerated catalyst within the upper and lower limits ofsaid predetermined temperature range for return of same to saidhydrocarbon conversion zone.
 3. The process of claim 2 furthercharacterized in that the control of the amount of heat removal in saidrelatively dense phase heat removal zone and thereby the temperature ofthe regenerated catalyst in the dense-phase fluid bed of said heatremoval zone is accomplished by: (a) providing heat-removal meanspartially immersed in said dense-phase fluid bed of said heat removalzone; and (b) manipulating the extent of immersion of said heat removalmeans in said dense-phase fluid bed.
 4. The process of claim 2 furthercharacterized in that the inlet temperature of said relativelydilute-phase combustion zone is raised by returning a part of saidregenerated catalyst collected and withdrawn from an upper locus of saidrelatively dilute-phase combustion zone to a lower locus of saidrelatively dilute-phase combustion zone.
 5. The process of claim 4further characterized in that a part of the hot regenerated catalystwithdrawn from an upper locus of said relatively dilute-phase combustionzone is mixed with said coke-contaminated fluid catalyst prior to theintroduction thereof into a lower locus of same combustion zone.
 6. Theprocess of claim 2 further characterized in that said regeneratedcatalyst in said relatively dense-phase heat removal zone and said hotflue gas ar contacted in said relatively dense-phase heat removal zone,at dense-phase fluid conditions, to withdraw heat from said hot flue gasand thereby produce flue gas possessing a lower temperature.